Japanese Laid-Open Patent Publication No. 2007-7832 discloses a swash bearing-type, power hammer drill that linearly drives a tool bit using an oscillating mechanism. The power hammer drill mentioned in the above publication, which serves as an impact tool, comprises a swash bearing-type oscillating mechanism that principally comprises: a rotary body, which is rotatably driven by an electric motor, and an oscillating member that carries out an oscillating movement in the longitudinal axis direction of the tool bit as the rotary body rotates. The power hammer drill is configured such that the rotational output of the electric motor is converted by the oscillating mechanism into linear motion that then linearly drives the tool bit. An inner rotor-type motor, which comprises a stator and a rotor disposed on the inner side of the stator, is used as the electric motor; a speed reducing mechanism reduces the rotational speed of the motor, and that rotation is transmitted to the rotary body.
The swash bearing type oscillating mechanism configured as described above is used in relatively compact hammer drills; however, in the case of such compact power hammer drills, there is a strong demand to improve the ease of operation by making the tool body lightweight.